On Tue, Feb 16, 2010 at 07:52:51PM +0900, iquiw wrote:
Is there any efficient way to convert M-length ByteString, Text or Vector into N-length one?
This is just a guess, but in vector at least it should be possible to use sized[1] to tell how much space should be allocated on the final vector. For example, something like the following *untested* code: import qualified Data.Vector.Stream.Monadic as S import qualified Data.Vector.Generic as G import Control.Applicative import Data.Vector.Stream.Size -- | The size should be the size of each v b. concatMapSized :: (G.Vector v a, G.Vector v b) => Size -> (a -> v b) -> v a -> v b concatMapSized size_each f v = let stream = G.stream v size = mult size_each (S.size stream) in G.unstream . flip S.sized size . S.concatMap (G.stream . f) $ stream mult :: Size -> Size -> Size mult (Exact n) (Exact m) = Exact (n*m) mult x y = maybe Max Unknown $ (*) <$> upperBound x <*> upperBound y I really don't know if this would improve or worsen performance, you should check the core and do benchmarks :). [1] http://hackage.haskell.org/packages/archive/vector/0.5/doc/html/Data-Vector-... -- Felipe.